1. Field of the Invention
The present invention relates to a thermal head, a thermal printer, and a manufacturing method for the thermal head.
2. Description of the Related Art
There has been conventionally known a thermal head for use in thermal printers (see, for example, Japanese Patent Application Laid-open No. 2009-119850). In the thermal head described in Japanese Patent Application Laid-open No. 2009-119850, a plurality of heating resistors are formed on a stacked substrate of a support substrate and an upper substrate, and power is supplied to pairs of electrodes connected to the heating resistors, thereby allowing the heating resistors to generate heat to perform printing on a thermal recording medium or the like.
In the thermal head, a cavity portion is formed at a position opposed to each of the heating resistors in a bonding portion between the support substrate and the upper substrate. The cavity portion functions as a heat insulating layer of low thermal conductivity to reduce an amount of heat to be transferred from the heating resistor toward the support substrate via the upper substrate, to thereby increase thermal efficiency and reduce power consumption.
Further, in the commonly-used thermal head, in order to supply the heating resistor with sufficient power from an external power source, the electrodes are designed in consideration of the electrical resistance from external input terminals to the heating resistor. As the ratio of the electrical resistance of the electrode to the electrical resistance of the heating resistor becomes larger, a larger power loss occurs by voltage drop of the electrical resistance from the external input terminals to the heating resistor. It is therefore necessary to decrease the electrical resistance of the electrode. The electrical resistance of the electrode can be decreased by thickening the electrode.
However, heat generated by the heating resistor diffuses also in the planar direction of the upper substrate via the electrodes. Further, when the electrode is thickened, the thermal conductivity of the electrode is increased. Therefore, the conventional thermal head has a problem that the heat insulating performance provided by the cavity portion cannot be fully utilized because the heat dissipates from the heating resistor in the planar direction of the upper substrate via the electrodes.